In the secondary processing technology of petroleum refining, the processing technology of fluid catalytic cracking (FCC) is highly regarded by refiners for its advantages of being able to treat feedstocks of inferior quality reasonably and economically, to produce gasoline having high octane number and bring in high economic benefits. In the past, the feedstocks used were mostly the gas oils produced from vacuum distillation, but over the recent decade, owing to the rise in crude oil price and crude oil per se tending to be heavier and so on, the refiners have turned more to processing or blending and refining of bottom oil from atmosphere distilling tower or residuum produced from the bottom of vacuum distilling tower in order to utilize the crude oil more effectively, get higher economic benefits and produce more light liquid oil products at the same consumption of crude oils. However, the metals, such as more nickel and a little iron and the like, are concentrated in the residuum and heavy oils, during catalytic cracking of the residuum and heavy oil, poisoning the catalyst for residuum and heavy oil catalytic cracking, thus causing the catalyst activity, as well as the light oil yield, to decrease. In order to maintain the activity of the catalyst at a certain level, the severely deactivated catalyst should be discharged at regular intervals, while making up large amounts of fresh catalyst. But, the catalyst is more expensive, about 2000 US dollars per ton, and the environment will be polluted by the piling-up metal contaminated catalyst. If the catalyst is regenerated for reuse, it will not only save a large sum of money from purchasing the catalyst and disposing the metal contaminated catalyst but also reduce the environment pollution.
In U.S. Pat. No. 4,293,403 (filed on Jan. 3, 1977, by Emmett H. Burk. Jr., et al.), a wet process for treatment of the metal contaminated catalyst is disclosed to demetalize such as nickel, iron and/or vanadium from the metal contaminated catalyst, comprising mainly three technological processes:
(1) sulfurizing: PA1 In the activation and reduction reactor, the catalyst contaminated by poisonous metals is contacted with the activation and reduction gases, so that the poisonous metal compounds deposited on the catalyst are activated by the activation gas, then reduced to metal simple substances under the action of the reduction gas; PA1 In the carbonylation reactor, the catalyst treated by activating and reducing is contacted with carbon monoxide gas to make the metal simple substances on the catalyst carbonylated to form gaseous metal carbonyls which are then transferred, separated from the solid catalyst and discharged from the reactor, thereby the activity of the catalyst is restored for reuse; and PA1 The discharged metal carbonyls gas is introduced into a thermal decomposition reactor and treated at a reaction temperature of 200.about.300.degree. C. and a pressure of 0.03.about.0.5 MPa (gauge) for 0.5.about.12 hours to get the gaseous metal carbonyls decomposed to carbon monoxide gas and solid metals, then the carbon monoxide is recycled back to the carbonylation reactor for reuse, and the metals are recovered.
Introducing hydrogen sulfide in a concentration of at least about 20% (v/v) into the metal contaminated catalyst under the conditions of a temperature of 500.about.1700.degree. F. (260.about.926.degree. C.) and a pressure (partial pressure of gas containing sulfur) of 0.05.about.3 MPa for a period of 1/4.about.20 hours, to convert the compounds of nickel and the like on the catalyst into metal sulfides; PA2 (2) oxidizing:
After treated by sulfurization, the catalyst is oxidized under the conditions of a temperature of 600.about.700.degree. F. (316.about.372.degree. C.) and a partial pressure of oxygen of 0.2.about.3 MPa for 25 minutes to convert the metal sulfides into soluble metal sulfates, sulfites, thiosulfates and simple sulfides; PA3 (3) washing: PA4 Adding sulfurous acid, sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide and a large amount of water to the catalyst which has been treated by oxidation, and washing repeatedly.
However, the process has to be carried out at a high temperature and in a corrosive medium containing sulfur compounds during the sulfurization, and also in a high concentration of H.sub.2 S (at least 20% (v/v)), therefore the requirements of material quality and corrosion resistance for the apparatuses are critical; furthermore, since the chemical agents with strong acidity and corrosivity, such as HNO.sub.3, HCl, H.sub.2 SO.sub.4, H.sub.2 O.sub.2 etc., have to be used, a waste liquor is turned out from washing, and thus a secondary pollution to the environment occurs, while the production cost will be increased and the active elements-rare earth oxides on the catalyst will be impaired.
Therefore, people are seeking to develop a novel process for treating and demetalizing the metal contaminated catalyst, which must be simple in technological process, not critical about the material quality of the apparatuses and not harmful to the active elements of the catalyst, and wherein no liquid is to be added and discharged and thereby no secondary pollution to the environment will occur.